1. Field of the Invention
The present invention relates to integrated voltage or current reference sources, and more particularly to precision reference sources capable of operating under the condition of lower feed voltage.
2. Description of the Prior Art
Conventionally, the Zener diode is widely used as a reference source. However, as is well known, Zener diodes have certain inherent breakdown voltage which undesirably restrict the capability of lower voltage use. On the other hand, a Bandgap reference has been developed. U.S. Pat. Nos. 3,617,859 and 3,887,863 disclose typical constructions of the Bandgap references. The Bandgap references also have certain inherent voltages caused by the extrapolated energy band-gap voltage of the semiconductor material at an absolute zero temperature (about 1.2 volts). Generally, this inherent voltage causes no problems, and therefore the Bandgap references are well used in any integrated circuits. However, the Bandgap references cannot work under the condition of feed voltage lower than 1.2 volts, and occupy a large chip area on an integrated circuit for keeping a high density ratio (about 10) of transistor current.